| 摘要 |
A surface-treated steel strip having improved weldability is provided, comprising a metallic Cr layer deposited on a steel strip to a weight of 50 to 150 mg/m<2>, a metallic Sn layer deposited on the chromium layer to a weight of 50 to 400 mg/m<2>, and a chromate coating layer deposited on the Sn layer and consisting essentially of 3 to 15 mg/m<2> of metallic Cr and 3 to 15 mg/m<2> of hydrated Cr oxide calculated as elemental Cr. The surface-treated steel strip is made by subjecting the cleaned surface of a steel strip to chromium electrodeposition, rinsing the Cr-deposited strip, subjecting the strip to tin electrodeposition in an acidic bath containing 1.5 to 10 grams per liter of Sn ion at a pH of lower than 0.5, rinsing the Sn-deposited strip, and subjecting the strip to chromate treatment in a chromate bath containing up to 50 grams per liter of CrO3 and sulfuric acid, a sulfate or fluoride at a current density of at least 10 A/dm<2>, thereby forming a chromate coating layer consisting essentially of metallic Cr and hydrated Cr oxide. |
